Polymérisation du lactide par des catalyseurs β-diketiminate de zinc et de magnésium

Les images de molécules ont été dessinées avec le logiciel Chemdraw version 11.0Le N,N’-Di(S-phenylethyl)-2-amino-4-imino-pent-2-ène, S,S-nacnacCH(Me)PhH, 2.1a, le N,N’-dibenzyl-2-amino-4-imino-pent-2-ène, nacnacBnH, 2.1b, et le N,N’- dibenzyl-2-amino-4-iminopent-2-chloro-ène, Cl-nacnacBnH, réagissent avec le Zn[N(SiMe3)2]2 pour former les complexes nacnacZnN(SiMe3)2 correspondants. En réaction avec l’isopropanol, ils forment les nacnacZnOiPr, 2.7a, 2.7b et 3.3. Tous ces complexes sont actifs en polymérisation du rac-lactide par une réaction de premier ordre en lactide. Les polymères obtenus montrent une préférence hétérotactique, avec une valeur de Pr = 0.84 – 0.87 (2.7a), 0.65 – 0.71 (2.7b) et 0,59 – 0,65 (3.3). Le changement du groupement N-alkyles de chiral vers achiral a permis de descendre la valeur de Pr. Cette baisse a été encore plus prononcée en présence d’un groupement électronattracteur à l’arrière du ligand. Un complexe analogue a été synthétisé en changeant la nature du centre métallique pour du Mg, ce qui a augmenté grandement la vitesse de réaction de polymérisation (de 1.5 h à 0.5 h pour 98 % de conv.). Le polylactide résultant (PLA) est atactique à température ambiante mais a montré une préférence isotactique à basses températures.N,N’-Di(S-phenylethyl)-2-amino-4-imino-pent-2-ene, S,S-nacnacCH(Me)PhH, 2.1a, N,N’-dibenzyl-2-amino-4-imino-pent-2-ene, nacnacBnH, 2.1b, and N,N’- dibenzyl-2-amino-4-iminopent-2-chloro-ene, Cl-nacnacBnH, react with Zn[N(SiMe3)2]2 to form the corresponding nacnacZnN(SiMe3)2 complexes. From further reactions with isopropanol nacnacZnOiPr, 2.7a, 2.7b and 3.3, were obtained. All complexes were catalytically active for the polymerisation of rac-lactide with apparent first-order reaction rates in lactide. Obtained polymers showed heterotactic preference, with Pr = 0.84 – 0.87 (2.7a), 0.65 – 0.71 (2.7b) and 0.59 – 0.65 (3.3). Changing N-alkyl substituents from chiral to achiral resulted in a drop in Pr. The value increased with an electron-poor substituant on the backbone. The Mg analogous complex greatly increased the polymerization rate (from 1.5 h to 0.5 h for 98 % conv.). The resulting polylactide (PLA) was atactic at room temperature, but showed a slight preference for isotacticity at lower temperatures

Coordination of a bifunctional ligand to a rhodium(III) dimethyl complex : Lewis acidity enhancement by chelation

The addition of the ambiphilic compound (Me2PCH2AlMe2)2 (1) to Cp*RhMe2(DMSO) (DMSO ) dimethylsulfoxide) (2) gives Cp*RhMe2(PMe2CH2AlMe2‚DMSO) (3‚DMSO). The addition of Lewis acids (LA) such as La(dbm)3 (dbm ) dibenzoylmethane) and AlMe3 to a solution of complex 3‚DMSO gives a competition reaction that results in the formation of LA‚DMSO and Cp*RhMe2(PMe2CH2AlMe2) (3). When heated to 40 °C, complex 3 ionizes to a putative zwitterionic species, Cp*Rh+Me(PMe2CH2AlMe3 -) (3′), which is converted to [Cp*Rh(Me)(µ2 -η2 -Me2PCH2)]2 (4) irreversibly. Spin saturation transfer experiments demonstrated that the rate of the methyl abstraction by the alane moiety was 0.76 ( 0.09 s-1 , while the rate of abstraction of the methyl in Cp*RhMe2(PMe3) by AlMe3 was 0.10 ( 0.02 s-1 . The zwitterionic species 3′ could be trapped in solution by addition of PMe3 to afford both Cp*Rh+Me(PMe3)(Me2- PCH2AlMe3 -) (5) and [Cp*Rh+Me(PMe3)(Me2PCH2AlMe2)]AlMe4 - (6). When compound 1 was added to complex 3′, the formation of the zwitterionic complex Cp*Rh+Me(η2 -Me2PCH2Al-Me2CH2PMe2) (7) was observed

Highly efficient and selective recovery of rare earth elements using mesoporous silica functionalized by preorganized chelating ligands

Separating the rare earth elements (REEs) in an economically and environmentally sustainable manner is one of the most pressing technological issues of our time. Herein, a series of preorganized bidentate phthaloyl diamide (PA) ligands was synthesized and grafted on large-pore 3-dimensional (3-D) KIT-6 mesoporous silica. The synthesized sorbents were fully characterized by N2 physisorption, FT-IR, 13C cross-polarization (CP) and 29Si magic-angle spinning (MAS) NMR, thermogravimetric analysis-differential thermal analysis (TGA-DTA), and elemental analysis. Overall, the grafting of PA-type ligands was found to have significantly improved the extraction performance of the sorbents toward REEs compared to the homogeneous analogues. Specifically, the sorbent modified with the 1,2-phtaloyl ligand shows high preference over lanthanides with smaller size, whereas the 1,3-phtaloyl ligand exhibits selectivity toward elements with larger ion radius. This selectivity drastically changes from the homogeneous models that do not exhibit any selectivity. The possibility of regenerating the mesoporous sorbents through simple stripping using oxalate salt is demonstrated over up to 10 cycles with no significant loss in REEs extraction capacity, suggesting adequate chemical and structural stability of the new sorbent materials. Despite the complex ion matrix and high ionic composition, the exposure of industrial mining deposits containing REEs to the sorbents results in selective recovery of target REEs

Conductive filament evolution dynamics revealed by cryogenic (1.5 K) multilevel switching of CMOS-compatible Al2O3/TiO2 resistive memories

This study demonstrates multilevel switching at 1.5 K of Al2O3/TiO2-x resistive memory devices fabricated with CMOS-compatible processes and materials. The I-V characteristics exhibit a negative differential resistance (NDR) effect due to a Joule-heating-induced metal-insulator transition of the Ti4O7 conductive filament. Carrier transport analysis of all multilevel switching I-V curves show that while the insulating regime follows the space charge limited current (SCLC) model for all resistance states, the conduction in the metallic regime is dominated by SCLC and trap-assisted tunneling (TAT) for low- and high-resistance states respectively. A non-monotonic conductance evolution is observed in the insulating regime, as opposed to the continuous and gradual conductance increase and decrease obtained in the metallic regime during the multilevel SET and RESET operations. Cryogenic transport analysis coupled to an analytical model accounting for the metal-insulator-transition-induced NDR effects and the resistance states of the device provide new insights on the conductive filament evolution dynamics and resistive switching mechanisms. Our findings suggest that the non-monotonic conductance evolution in the insulating regime is due to the combined effects of longitudinal and radial variations of the Ti4O7 conductive filament during the switching. This behavior results from the interplay between temperature- and field-dependent geometrical and physical characteristics of the filament.Comment: 8 pages, 4 figure

Observation of Highly Nonlinear Resistive Switching of Al2O3/TiO2-x Memristors at Cryogenic Temperature (1.5 K)

In this work, we investigate the behavior of Al2O3/TiO2-x cross-point memristors in cryogenic environment. We report successful resistive switching of memristor devices from 300 K down to 1.5 K. The I-V curves exhibit negative differential resistance effects between 130 and 1.5 K, attributed to a metal-insulator transition (MIT) of the Ti4O7 conductive filament. The resulting highly nonlinear behavior is associated to a maximum ION/IOFF ratio of 84 at 1.5 K, paving the way to selector-free cryogenic passive crossbars. Finally, temperature-dependant thermal activation energies related to the conductance at low bias (20 mV) are extracted for memristors in low resistance state, suggesting hopping-type conduction mechanisms.Comment: 4 pages, 4 figures, IEEE 14th Nanotechnology Materials & Devices Conference (NMDC 2019

Technology platform for the fabrication of titanium nanostructures

Abstract : This paper presents two approaches for the fabrication of top-down titanium nanostructures. The first approach involves electron beam lithography followed by a tailored titanium plasma etching. The two main challenges of this process lie in the optimization of the negative tone Ma–N electroresist resolution and in the definition of a controlled titanium etching process for titanium patterns less than 20 nm thick and wide. The second proposed approach is a damascene process where the titanium nanostructures are buried in the oxide. Very shallow and narrow (20 nm × 20 nm) trenches are first patterned in the oxide and nanostructures are obtained by planarization of an evaporated titanium film. The dimensions of the structures are defined by the electron beam lithography resolution and the etching recipe. The third dimension is given by the titanium or any other metal thickness and can be controlled down to few nanometers thanks to the planarization step

Quantifying migratory capacity and dispersal of the invasive tench (Tinca tinca) in the St. Lawrence River using otolith chemistry

ABSTRACT The study of distribution and dispersal of invasive fishes is challenging during the early stages of invasion. Quantification of trace elements incorporated into fish hard parts represents an innovative technique for this task. Otolith chemistry has been used to describe fish stock structure, migratory behaviour and to support the management of several species. We used otolith chemistry to study the dispersal and population structure of tench (Tinca tinca), an invader in the St. Lawrence River. Tench movements throughout the invaded portion of the system were reconstructed using a Random Forests algorithm. The results showed that, despite the presumed limited dispersal capacity of the species, tench are capable of extensive migratory movements (up to 250 km). The variability in migratory patterns among individuals, including both short- and long-distance movements, supports a stratified diffusion. Such a strategy may explain the successful invasion of tench in the St. Lawrence River ecosystem. Our study represents a flexible framework for the study of tench ecology in its invaded and native range, as well as for other freshwater invasive fishes. RÉSUMÉ L’étude de la répartition et de la dispersion de poissons envahissants durant les premières étapes de l’envahissement n’est pas chose facile et, pour ce faire, la quantification d’éléments en traces incorporés dans les parties dures de poissons constitue une approche novatrice. La chimie des otolites a été utilisée pour décrire la structure de stocks et le comportement migratoire des poissons, ainsi que pour appuyer la gestion de plusieurs espèces. Nous avons utilisé la chimie des otolites pour étudier la dispersion et la structure de la population de tanche (Tinca tinca), une espèce envahissante dans le fleuve Saint-Laurent. Les déplacements des tanches dans toute la portion envahie du système ont été reconstitués à l’aide d’un algorithme de forêts aléatoires. Les résultats montrent que, malgré une capacité de dispersion limitée présumée pour cette espèce, les tanches sont capables d’effectuer de grands déplacements migratoires (jusqu’à 250 km). La variabilité des habitudes migratoires d’un individu à l’autre, qui comprend des déplacements tant sur de longues que sur de courtes distances appuie une stratégie de diffusion stratifiée. Une telle stratégie pourrait expliquer l’envahissement de l’écosystème du fleuve Saint-Laurent par la tanche. Notre étude offre un exemple d’approche polyvalente pour l’étude de l’écologie de la tanche dans ses aires de répartition indigène et envahis, mais aussi chez d’autres poissons d’eau douce envahissants

Cerebrovascular and blood-brain barrier impairments in Huntington's disease: Potential implications for its pathophysiology: Vascular impairments in HD

ObjectiveAlthough the underlying cause of Huntington's disease (HD) is well established, the actual pathophysiological processes involved remain to be fully elucidated. In other proteinopathies such as Alzheimer's and Parkinson's diseases, there is evidence for impairments of the cerebral vasculature as well as the blood–brain barrier (BBB), which have been suggested to contribute to their pathophysiology. We investigated whether similar changes are also present in HD.MethodsWe used 3‐ and 7‐Tesla magnetic resonance imaging as well as postmortem tissue analyses to assess blood vessel impairments in HD patients. Our findings were further investigated in the R6/2 mouse model using in situ cerebral perfusion, histological analysis, Western blotting, as well as transmission and scanning electron microscopy.ResultsWe found mutant huntingtin protein (mHtt) aggregates to be present in all major components of the neurovascular unit of both R6/2 mice and HD patients. This was accompanied by an increase in blood vessel density, a reduction in blood vessel diameter, as well as BBB leakage in the striatum of R6/2 mice, which correlated with a reduced expression of tight junction‐associated proteins and increased numbers of transcytotic vesicles, which occasionally contained mHtt aggregates. We confirmed the existence of similar vascular and BBB changes in HD patients.InterpretationTaken together, our results provide evidence for alterations in the cerebral vasculature in HD leading to BBB leakage, both in the R6/2 mouse model and in HD patients, a phenomenon that may, in turn, have important pathophysiological implications. Ann Neurol 2015;78:160–17

A Solve-RD ClinVar-based reanalysis of 1522 index cases from ERN-ITHACA reveals common pitfalls and misinterpretations in exome sequencing

Purpose Within the Solve-RD project (https://solve-rd.eu/), the European Reference Network for Intellectual disability, TeleHealth, Autism and Congenital Anomalies aimed to investigate whether a reanalysis of exomes from unsolved cases based on ClinVar annotations could establish additional diagnoses. We present the results of the “ClinVar low-hanging fruit” reanalysis, reasons for the failure of previous analyses, and lessons learned. Methods Data from the first 3576 exomes (1522 probands and 2054 relatives) collected from European Reference Network for Intellectual disability, TeleHealth, Autism and Congenital Anomalies was reanalyzed by the Solve-RD consortium by evaluating for the presence of single-nucleotide variant, and small insertions and deletions already reported as (likely) pathogenic in ClinVar. Variants were filtered according to frequency, genotype, and mode of inheritance and reinterpreted. Results We identified causal variants in 59 cases (3.9%), 50 of them also raised by other approaches and 9 leading to new diagnoses, highlighting interpretation challenges: variants in genes not known to be involved in human disease at the time of the first analysis, misleading genotypes, or variants undetected by local pipelines (variants in off-target regions, low quality filters, low allelic balance, or high frequency). Conclusion The “ClinVar low-hanging fruit” analysis represents an effective, fast, and easy approach to recover causal variants from exome sequencing data, herewith contributing to the reduction of the diagnostic deadlock